In many applications, such as transmitters, couplers, antennas, test equipment, etc., it is desirable to provide high power RF switches useable from DC to high RF frequencies. In general, evacuated electromechanical RF relays may be constructed which will provide this function but they are relatively slow and very costly. RF pin diode switches are useful in switching high RF frequencies but they are not useful from DC to low RF frequencies and are generally not capable of switching high power.
A high power RF relay switch which combines the best functions of RF relays and RF pin diode switches is disclosed in U.S. Pat. No. 4,249,150, entitled "High Power RF Relay Switch", issued Feb. 3, 1981. This high power RF relay switch includes a reed relay having pin diodes connected in parallel therewith and forward biased for conduction when the reed relay is actuated. The pin diodes are reverse biased once the reed relay closes so that they are removed from the circuits. The biasing is performed by a semiconductor switching circuit which includes a capacitor for timing. However, it has been found that this circuit has some serious drawbacks in that it latches up at certain RF frequencies and does not reverse bias the pin diodes. Since the pin diodes are continuously conducting the high power RF they burn out very rapidly.